Thermocouple recorder

ABSTRACT

This disclosure is concerned with a novel digital multi-point recorder that is microprocessor-controlled and enables impact printing from in back of the recorder paper to provide a front visible flat print-out of pages of on-line running summary data suited for operator viewing in industrial and similar locations, and providing a record for direct use in reports and logs.

This is a divisional application of Ser. No. 071,947, filed Sept. 4,1979, now U.S. Pat. No. 4,329,693.

The present invention relates to methods of and apparatus for datarecording and the like, being more particularly directed to therecording of data such as that produced during measurement, control orproduction monitoring and similar operations, and documenting therecorded information in a format suitable for direct use in logs andreports and in related usages.

In many industrial, research and similar processes, it has long beendesirable to have a data recording apparatus positioned where theoperator can readily view the most recent values of important parametersunder monitor, such as, for example, temperatures, pressures, flowrates, motor speeds, and many other quantities. The recorded data,moreover, must be presented in a manner which permits the operator toobserve changes in the data, and the recorder apparatus itself must havea physical design which can operate reliably in industrial and similarenvironments. Among the recording apparatus heretofore used for suchpurposes have been the multi-point or pen recorder which printed aseries of marks or a continuous line on a paper scroll, with theleft-to-right location of the marks or lines representing the value ofthe data being recorded. This type of equipment, however, is subject todisadvantages of limited resolution, interpolation errors, and cloggedpens, and the requirement for special recording chart paper. Theoperator, furthermore, is required to interpret the analog meaning ofthe record and to convert the same to digital value, where required.

It is also often necessary, in addition, that the parameters beingrecorded or logged for display to the operator be summarized in a formsuitable for ultimate presentation in a written report or the like. Atabular form is often desirable. In the past, accordingly, the data hasbeen extracted from the recorder charts and summarized or transcribedmanually; or, in more elaborate systems, the data has been transmittedto a computer system in a different part of the plant to be summarizedfor inclusion in a report.

Other data logging apparatus has involved data acquisition in the formof digital printing on an adding machine-like tape; which not onlyinvolves the disadvantage of leafing through long tapes to determinetrend comparisons and the like, but is decidedly unsuitable for directuse in reports.

A first important step in obviating some of these problems anddisadvantages was provided by the "Digistrip" multipoint recorder of theassignee of the present invention, as described, for example, inBulletin DR75 (July 6, 1975) of Kaye Instruments of Bedford, MA; thisrecorder employing impact paper recording of direct digital print-out.While improving upon direct process recording, this system was stillrestricted in the operator's visual access to the recording chart and inthe quantity of data available at a glance for comparison, and did notprovide on-line summaries or similar data compilations, and not in aformat directly useable in reports and like documents.

An object of the present invention, therefore, is to provide a new andimproved data recording apparatus and method that lend themselves toutilization particularly, though not exclusively, in industrial plantenvironments, and that obviate the above-mentioned and other problems,providing for the clear presentation of data which has been recorded inthe recent past such that an operator can readily observe current valuesand trends, and in a digital, tabular format suitable for directinsertion in reports.

In accordance with the invention, it is important that the printed pagebe displayed clearly, including the last line of printout, and that theapparatus be designed to be compatible with other requirements ofcontrol room or other production or research environments. The frontface of the apparatus should be reasonably flush, with the recorderchart flat against the same, and housed in an enclosure which can bemounted in the control panel of conventional identical instrumentationequipment racks. Another objective is to provide data recordingapparatus which is as simple, yet as reliable as possible, and with theprinter mechanism designed with a minimum of electro-mechanical parts,and the electronic circuitry, with minimum power dissipation andtemperature rise performance within the semi-sealed enclosure.

A further object of the invention is to provide a novel digitalmultipoint recorder that is provided with recording and calculatingcapabilities that approach those of a mini-computer-based dataacquisition system, embodying a microprocessor-aided page printer thatproduces an on-line running summary not only ideally suited for operatorusage but for enabling the same record to be directly inserted into logsand reports.

Still another object is to provide such a novel recorder that is ofparticular advantage with temperature measuring apparatus and the like,among other sensors.

An additional object is to provide a new and improved recorder andsub-combination portions thereof of more general utility, as well.

Other and further objects will be explained hereinafter and will be moreparticularly delineated in the appended claims.

In summary, from one of its important aspects, the invention embracesprinting apparatus for use with impact-sensitive paper having, incombination, means for mounting the paper as a continuous longitudinallyextending substantially flat sheet to be directly viewed from one facethereof, print head means disposed at a predetermined location on theother face of the sheet, and means for causing the print head means toimpact against the said other face along transverse lines at saidpredetermined location to produce visible printing on the said one face.Preferred or best mode embodiments, and details of the apparatus andsub-assemblies of the same, are hereinafter presented.

The invention will now be described with reference to the accompanyingdrawings, FIG. 1 of which is an isometric view, partly broken away toillustrate details of construction, of a preferred embodiment;

FIG. 2 is a combined block and schematic circuit diagram of the paperdrive for the system of FIG. 1;

FIG. 3 is a waveform diagram relating to the performance of FIG. 2;

FIG. 4 is a fragmentary isometric view showing the utilization of therecording system of FIG. 1 with a temperature-sensing array; and

FIG. 5 is an isometric view showing the front door and data acquisitionboard of the recording system.

Referring to FIG. 1, the invention enables the before-mentioned highlydesirable result of positioning the recorder printed page as close tothe front face of the apparatus as possible for the most facile viewingby the observer, by positioning the print head 1 at a predeterminedlocation near the bottom and on the opposite face of the paper 2 fromthe observer, such that it strikes or impacts upon the paper from therear. The paper 2 is mounted to travel longitudinally vertically,traversing between the print head 1 and a platen 3 such that the impactforce of the print head 1 is absorbed by the platen 3 through the paper2. The print head 1 is transversely horizontally driven from side toside by a single motor 4 running in one direction. The motor 4 drives achain 5 through a slider-pin mechanism 6, with the print head 1 ridingupon a set of guides 7 to maintain constant spacing between the printhead 1 and the platen 3. While the terms "vertically", "horizontally"and "bottom" are illustrative of a preferred orientation, they aregenerically used herein to connote equivalent relative positions, aswell. Suitable impact-sensitive chart paper for enabling this reverseprinting (ink-impregnated pressure sensitive, or the like) is, forexample, type SC White #17 of NCR Corporation.

A light source and optical sensor 1', mounted rearwardly with the printhead 1, detects, as the head transversely traverses the apparatus,alternate transparent and opaque vertical lines on a fixed transversestrip 8, extending beyond the width of the printed page, and serving asan optical fence, with one end completely opaque, and the other endcompletely transparent. A special electronic circuit detects eachtransition from transparent to opaque as a potential print position, andthe printer logic will cause the appropriate character to be printed.When the print head 1 reaches either end region and does not detect atransition for a pre-determined period of time, an associated controlcircuit will continue to print the next line of data or turn off themotor if there is no further data to be printed. By sensing whether thestrip is completely transparent or completely opaque, the printer logicis informed whether the print head 1 is at the left or right margin ofthe page so that, unlike other prior printing apparatus, there is noneed to have separate sensors to determine when the print head 1 is at amargin, and to determine which margin.

The control logic is designed such that printing can occur with theprint head 1 travelling in either transverse direction, so that it isnot necessary to bring the print head 1 back to the left margin eachtime before starting a new line. The construction of the invention thuseliminates the typical carriage return operation of most printers. Ifthe next line to be printed is already available, the motor 4 drivingthe print head 1 does not stop when a margin is detected, but itcontinues to drive the print head 1, and the slider-pin mechanism 6automatically reverses the direction of the print head 1. With this typeof mechanism, the next complete line to be printed is stored in thehereinafter described microprocessor memory before the printingoperation of that line is started.

Exemplary components for this system are, for example, the Model IPM 129print head of Victor Comptometer Corporation, which includes an opticalsensor.

Another important feature of the invention enabling its novel resultsresides in the paper feed and take-up mechanism contained within theinstrument enclosure. Paper moves continuously from the paper supplytray 10 through paper guides 9. It then passes between the platen 3 andthe print head 1, as before described, vertically upward as asubstantially flat sheet through a paper tension mechanism such as sidefriction clips 11 to the set of feed tractors 12, 12' which pull thepaper from the feed tray when a new line has been printed and positionit at the proper location for the next line. The print head 1 and theplaten 3 must be oriented so that the motion of the flat sheet of paperby one vertical line space will move the previous printed line intoview. This permits an observer immediately to view the current datawhich has just been printed, unlike other types of printers. In order tomaintain even line spacing, the tension clips or other mechanism 11 mustmaintain proper and uniform tension on the paper at the bottom of theapparatus, the same also preventing the paper from moving in theleft-to-right direction and thereby providing a printed page with thedesired vertical column alignment. The paper tractors 12, 12' areoperated by a single stepping motor 13 through belt 14 and pulley drivemechanism 15.

Details of the printer mechanism, carriage controls, sensor and othercircuit and constructional details are not presented in order to avoiddetracting from the novel features of the invention with well-knownmechanisms; but reference to other suitable constructions is made, forexample, to the Kaye Instruments "Digistrip Recorder Installation,Operation and Maintenance Manual", dated April 1978.

The electrical circuit to drive the stepping motor 13 has been designedin accordance with the best mode of the invention to minimize the powerdissipated, thereby minimizing the temperature rise of the motor and theinterior of the semi-sealed enclosure. The stepping motor drive circuitpreferably operates under the principle of pulse-width modulation of thevoltage across the stepping motor, as later described in connection withthe preferred form of FIG. 2. During the time the tractor mechanism isat rest, a very low duty cycle pulse train is used to provide detentaction of the mechanism. During the time the tractor mechanism isadvancing the paper, a full duty cycle with a voltage which is higherthan--more than twice--the rated voltage

of the stepping motor is used to provide maximum and higher-than-ratedtorque. The stepping motor 13 is accordingly operated with lower powerconsumption when stationary than when moving to attain the aboveresults. Another feature of this circuit allows positioning of the pageto be maintained during a power-off/power-on sequence. This facilitatesthe pagination of the paper even if a power failure occurs.

A typical stepping motor suitable for use in accordance with theinvention, such as the Series 82700 of North American Philips ControlsCorporation, is divided into two sections, each of which has two sets ofwindings. In the circuit shown in FIG. 2, the first section containswindings 37 and 39, and the second section, windings 41 and 43. Eachwinding is driven by a drive circuit D the output of which is thecollector of a transistor in the common-emitter configuration. When eachdrive circuit D is activated, current flows from the supply voltageV_(D) through the corresponding motor winding and through the outputtransistor to ground. When the driver is deactivated, the currentflowing through the winding inductance is shunted back to V_(D) througha corresponding shunt diode d. This current will decay to zero in a fewmilliseconds due to the winding resistance and the diode forward voltagedrop.

During normal operation one winding of each section is activated.Stepping is performed by making a transition from one winding to anotherin one section. The next step would be performed by making a transitionin the other section. Flip-flop 31 controls which of windings 37 or 39is activated, while flip-flop 32 controls which of windings 41 or 43 isactivated.

The circuit of FIG. 2 is placed in its quiescent or non-stepping stateby the reset input to edge-triggered flip-flop 30, or as a naturalresult of the completion of a step operation. Flip-flop 30 serves as amaster control in association with oscillators 34 and 35 and resetsfurther flip-flops 31, 32 and 33. While in the quiescent state, theflip-flop 30 is in the off state, and, in turn, resets flip-flops 31, 32and 33, and resets oscillator 34 and enables oscillator 35. Oscillator35 has a time asymmetrical output which is low for 10 microseconds(μsec) and high for 500 μsec. In the quiescent state, only windings 37and 41 are activated. The drivers place V_(D) across windings 37 and 39for 10 μsec out of each 500 μsec period. The current in the windings 37and 41 does not fall to zero, however, since the winding inductance incombination with the associated shunt diode d keeps current flowingbetween drive pulses. In this manner, sufficient current is provided tothe stepping motor to provide detent action on the paper while the powerdissipated is greatly reduced from that required during stepping. Thus,V_(D) can be two or more times the rated voltage of the stepping motorwithout causing overheating.

When the present input to master control flip-flop 30 is pulsed, asshown in the top waveform "30" of FIG. 3, the stepping operation isinitiated. For this mechanism, eight transitions of the winding drivecircuits are required to move the paper one line space, FIG. 3indicating the sequence of events for the line space operation, withtime periods T₀ through T₉ indicated at the bottom. At time T₀, thecircuit is in the quiescent state with the output of gate circuits 36and 40 pulsed by the output 35Q, FIG. 3, of oscillator 35, FIG. 2. Whenthe preset pulse is received, flip-flop 30 turns on at 30Q, oscillator35 is reset and oscillator 34 is enabled at 34Q. Oscillator 34 has aperiod of approximately 10 msec, and the Voltage V_(D) is placed acrosswindings 37 and 41 with full 100% duty cycle. This brings the windingcurrents up to a high level to maximize stepping torque. Oscillator 34clocks respective flip-flops 31 and 32 at 31Q through the necessarysequence of outputs. After four oscillator pulses from 34Q, flip-flop 33turns on as shown at 33Q. After an additional four oscillator pulses,flip-flop 33 turns off, in turn turning off master control flip-flop 30and placing the control circuit in the quiescent state once again. Theoutputs of gates 36 and 40, respectively operating through the drivers Dconnected with windings 37 and 41, are shown at 36 Out and 40 Out inFIG. 3; and the outputs of circuits 38 and 42, respectively connectingthe Q outputs of flip-flops 31 and 32 to operate the drivers D connectedto windings 39 and 43, are illustrated at 38 Out and 42 Out,respectively.

The reset input to the master control flip-flop 30 is used to preventpartial stepping of the circuit when power is turned on by immediatelyplacing the circuit in the quiescent state, thus preventing steppingwhen power is turned on and, in turn, facilitating the paginationprocess whereby the paper is held in the same position after a powerfailure as when power failed.

Unlike conventional line printers, which have available a large verticaldescent to facilitate folding the fanfold paper in the proper fashion,the apparatus of the present invention embodies special means to assurea proper folding of the paper within the limited dimensions of theenclosure. These means include an upper electro-static discharge andguide bar 16 and a paper receiver tray 17 which, in accordance with theinvention, must be positioned at a rather critical angle inclined to thehorizontal of between substantially 10° and 20°, in order to fold thepaper properly with a very limited vertical drop of less than, say, 7inches, more or less. With fanfold type paper, and the paper receivingtray thus located at such a height of less than about 7 inches below themaximum vertical height of the path travelled by the paper, theinclination of the said tray toward the direction from which the paperissues at the said acute angle from the horizontal causes the automaticfolding storage.

A feature which is not essential to the operation of the apparatus, butwhich adds a desirable character of low noise, is a platen 3 constructedof a composite of alternating metallic strips and vibration-dampingmaterial.

The electronics to control all printer operations is shown on a singleprinted circuit board 18 containing a microprocessor and all of therequired logic and memory. The printer mechanism can, of course, operateindependently of the data acquisition portion of the apparatus, if sodesired.

Referring to FIG. 5, the data acquisition portion on printed circuitboard 50 has an independent microprocessor which controls all operationsother than the printing of the data. In accordance with a preferred formof the invention, three types of memory are employed in the dataacquisition logic. The read-only memory portion 51 is used to storepermanently the programmed instructions to direct the data acquisitionfunctions, and also contains tables which are used for conversion ofdigital voltage data into the proper engineering data. A second portionof memory 52, called non-volatile random access memory is used to storeuser-programmed parameters such as the types of input, the frequency ofprinting, acceptable limits of data and identifying headers to beprinted at the top of each page. The third type of memory 53 is calledrandom access memory and is used to store the real-time data beingprocessed from the analog inputs to the system, as is well-known.

The overall structure of the microprocessor logic on printed circuitboard 50 is preferably directed by a "task manager" of the typedescribed in an article entitled "A Task-Scheduling Executive Programfor Microcomputer Systems" by David A. Townzen, appearing in ComputerDesign, June, 1977, pp. 194-202. This task manager is an efficient meansof controlling task priorities so that a more important task of higherpriority will temporarily interrupt a task of lesser priority in orderto provide service on a real-time basis.

Suitable microprocessor apparatus is the type 8085 manufactured by IntelCorporation, with memory of the types 2716, 2114 and 5101 of IntelCorporation, or other equally well-known microprocessor apparatus.

As an example of a resulting page of summary data directly useable forreports and the like and stemming from the microprocessor-printer of theinvention (81/2×11 inch fanfold paper, for example), up to five linesmay be made available on the sheet for customized header identification,each line having 128 characters corresponding to a field of 8 charactersfor each of 16 channel positions. Conventional customer-programmedalpha-numeric messages can be introduced to a conventional keyboard 54,located at the bottom of the front panel of FIG. 5, for example, suchthat the microprocessor enables the automatic printing of the same atthe top of every new fanfold page sheet. Suitable keyboard control isprovided by a Brady Corporation Lite Touch (TM) panel operating inconjunction with an Intel Corporation type 8279 keyboard interfacemodule. Programming of the header takes only a few minutes using suchfront panel keyboard entry. The apparatus may provide one to four linesof data, for example, to be printed in normal engineering units as ablock, with a blank line inserted after each block to separate the datacorresponding to a single scan, if desired. When there are too few linesremaining at the bottom of a page to print a complete block, the programmay enable the paper automatically to advance to the top of the nextpage for header printing. The header printout may also automaticallyinclude a day's register printed in the time field locations. Alarms maybe indicated by an asterisk printed in the data field of the alarmchannel, and the types of printed data may be identified by analphabetic character representing the appropriate engineering units, andmatching that used on the front panel display, printed as the lastcharacter in each channel's data field. Not counting header and marginspace, approximately 40 lines per page can be available with theabove-described fanfold paper for recording data. With 16 channelsprinted per line, 96,000 readings can be recorded on a typical stack ofpaper having about 150 pages.

The use of a microprocessor and its associated logic permits each userto program the apparatus to satisfy particular requirements mosteffectively, and also makes possible several new and important featuresin the data acquisition portion of the apparatus of the invention; inparticular, a novel technique for automatically assuring that theanalog-to-digital conversion circuit maintains a proper zero level. Toillustrate this feature, the example of the before-mentioned mostadvantageous use of the recorder system of FIGS. 1, 4, and 5 withtemperature sensors, such as thermocouple arrays, will be presented.

An analog-multiplexer 23, shown in FIG. 4, is provided with one extraswitch SW1 with a known zero voltage input. The microprocessor logic isdesigned, as is well known, to read that extra input periodically duringthe multiplexing sequence, convert same to digital form by means of ananalog to digital converter 19, and store the value as an offset whichmust be subtracted from the other input voltages. In order to obtaingreater stability of the zero level, several successive readings of thiszero input are maintained in memory and averaged. The average offset issubtracted from all other input signals. Suitable averaging andsubtracting is performed by the microprocessor.

In the exemplary showing of application to thermocouple sensing, FIG. 4also illustrates an improvement in the art of uniform temperaturereferences for thermocouple inputs such as that described in U.S. Pat.No. 3,648,523. The sensor system of FIG. 4 employs a bar 21 of a highlythermal conductive material, such as aluminum, having opposing flatsurfaces provided with a thin insulating coating on the surface 21',such as aluminum oxide, and which is in intimate thermal contact withthe printed circuit board mounting screw terminal shafts 25 of all ofthe input terminals 22. The design permits the insertion of theseterminals into a printed circuit board 23 and the insertion of atemperature sensor R1 into the highly conductive bar so that allterminals, as well as sensor R1, are maintained at very nearly the sameor equal temperature. The sensor which monitors the terminal temperatureis read as a separate input.

In accordance with this improvement, moreover, a singletemperature-sensitive resistor R1 made of a material having knownresistivity versus temperature characteristics is placed in series witha manually-adjustable resistor R2. A precision voltage source Vmaintains a constant voltage across the series connection of the tworesistors. With the temperature sensitive resistor R1 at a knowntemperature, the other resistor R2 is manually adjusted to provide apre-determined value of voltage across the temperature-sensitiveresistor. This single adjustment assures that the proper value ofvoltage will be produced across the temperature sensitive resistor atall temperatures within the operating range of the apparatus.

The microprocessor logic before described automatically adds the properreference voltage for each type of thermocouple corresponding to thetemperature of the input terminals as determined by reading the value ofvoltage appearing across the temperature-sensitive resistor.

While the incorporation of these improvements with the microprocessorcontrol of the novel recorder of the invention has been illustrated byreference to temperature measurements, moreover, it will be apparentthat other types of sensors, controls and data-generating sources mayalso be readily employed with the novel digital multipoint recordingtechnique and system of the invention; and that further modificationswill also suggest themselves to those skilled in this art, and areconsidered to fall within the spirit and scope of the invention asdefined in the appended claims.

What is claimed is:
 1. For use with printing apparatus and the like forrecording digital data generated from analog inputs from a plurality oftemperature sensing elements such as thermocouples, apparatus whereinsaid analog inputs are supplied to a printed circuit board by amultiplicity of printed circuit board mounting screw terminals havingshafts, means for maintaining the mounting screw terminals withsubstantial equality of temperature comprising a central bar of highthermal conductivity having opposing flat surfaces provided with a thinlayer of electrical insulation, and with the screw terminal shaftsbonded in intimate thermal contact with said surfaces.
 2. Apparatusaccording to claim 1 further comprising a discrete temperature sensor inintimate thermal contact with the bar for monitoring the temperature ofthe bar, and means for providing a signal representative of saidtemperature.
 3. Apparatus according to claim 2, wherein said temperaturesensor comprises a temperature-sensitive resistor inserted into the bar.4. Apparatus according to claim 3, wherein the signal providing meanscomprises a reference voltage source and a resistor connected in serieswith said temperature-sensitive resistor, and means for measuring avoltage across said temperature-sensitive resistor.
 5. Apparatusaccording to claim 4 further comprising microprocessor means responsiveto said measured voltage for automatically adding a reference voltagerepresentative of said temperature to said analog inputs.